Owing to interventions, the prevalence of malaria has declined in Tanzania. Klejnstrup et al. analyzed 15 years' worth of data on malaria rates, along with school achievement data for more than 200,000 children. They found that children born in periods with higher prevalences of malaria struggled more with numeracy and English literacy than counterparts at less risk of malaria. The effect of a malaria-free childhood on educational outcomes rivaled the effects of smaller class sizes and better-trained teachers.